Loudness of firing with and without pellet

[airgunfans]

I have a .22 Huben K1 shooting JSB Beast ( 34 grain ) at 984 fps. With the original shroud, the loudness of firing just air and firing pellet is roughly the same although the sound of firing air is mainly a “thrump” and that of firing pellet has a cracking “pakkk” mixed into it. I was firing at a large bag of old clothes so there is essentially no sound of the target being hit.

I have recently made a DIY silencer consists of an aluminum tube measuring 4cm diameter x 21 cm length with three chambers inside. The baffles are 2mm thick steel washers with 7mm hole. When firing unloaded, the rifle is a lot quieter. I would say the sound level is just 1/3 of the original level. However, the sound of firing pellet is a lot louder and is not much different from the original level.

May I know if this is normal ? Will a bigger silencer suppress the sound of firing pellets ?

 

[badammo]

Firing without a pellet the air will lose pressure rapidly as it moves down the bore since it has no restriction. Firing a pellet the pellet restricts the air so there is much more pressure at the muzzle and a louder thump sound.

 

[milacik]

maybe it is related to the side vents, without those I would expect it to be the other way round. louder without the pellet

plus you hear the pellet flying

 

[Altair-uy]

Silencers are not so easy as puting a tube with some baffles, I would suggest to buy a good one like the donny and problem solved with ease

 

[MScottLeeman]

...as a side note,firing With a pellet has been theoretically proven to be Much more enjoyable.

 

[milacik]

What did you use for baffles bootle caps? maybe they just rattle

 

[airgunfans]

...as a side note,firing With a pellet has been theoretically proven to be Much more enjoyable.

Certainly but it has to be neighbor friendly in the first place .....

 

[airgunfans]

What did you use for baffles bootle caps?

maybe they just rattle

The end cap is screw-on and baffles are separated by aluminium tube spacers. I don't think it's rattle as the spacers and baffles are pressed tightly against each other.

 

[airgunfans]

Silencers are not so easy as puting a tube with some baffles, I would suggest to buy a good one like the donny and problem solved with ease

I have made another DIY silencer for my Alecto pistol and it works great. The sound levels of firing air and pellet are the same. Just wondering why this one is not so.

Yes, I would like to try out DonnyFL silencers but unfortunately they don't ship outside US

 

[airgunfans]

..... plus you hear the pellet flying

That's a good point that has never come across my mind. The pellet was flying at 300 m/s which is close to the speed of sound ( 330 m/s ). Silencers cannot suppress the sound made by the pellet but just that made by the expansion of compressed air behind it . I will try to lower the fps to well below sonic speed and try again. 

 

[airgunmonkey]

I would suggest that, instead just put spacers between the washers, get a smaller diameter spacers ( hair curlers are 2cm in diameter) wrap with a sort of screen and cotton until reaches the ID of the silencer tube and you are good to go, just spacers wont suppress/dampening the sound as there is nothing to absorb the sound coming out of the barrel, make sure when wrapping the cotton around the curlers is nice and compressed and very snugly in the tube (not over tight), use cotton roll as it's easy to cut the length of the spacer and normally they are around 1/2" thick. That will damp the sound a lots. Also, sometimes is better use washers with a slightly larger hole, like 8mm, that helps the air/sound flow and expand, instead of compressing and exiting on a smaller whole causing a high pitch sound.

 

[airgunmonkey]

I had a Huben K1, also I would tune down the power a bit to around 950/960fps maybe 1 or 2 clicks on the power wheel, all that won't quiet the gun whisper quiet but it will tame it.

They are very powerful guns.

 

[steve-l]

I also made my own moderator for the same reason you did. It is always better to buy than to make from an economical view point, but in our case, we had no choice. However, my results were excellent. Design makes a big difference as well as precision. I have a machine shop and all the right tools. I made the moderator for my FX Crown in .25. My moderator has a 48 mm OD, 20 cm overall length with 4 internal chambers So my silencer is slightly larger in OD and 1 mm shorter than yours. My barrel has a choke that reduces the pellet diameter to .241". I allow .020" (.5 mm) clearance at the baffles. The first chamber is 10% larger in volume than the extended shroud internal volume. The remaining internal volume is divided equally by the remaining two baffles (3 chambers). My baffles are conical at a 45 degree angle with the cone facing the breech. My forward end cap is also conical internally, just like the baffles. The whole assembly is held together by 3 5mm studs that extend end to end. The baffles are held in position by aluminum, thin wall tubular spacers. To assure adequate and equal spacer/baffle compression, 6 Belleville spring washers are used on the 3 studs. The components were hard anodized black and assembled, the moderator weighs 354 grams. It mounts to the Crown shroud using a 1/2"-20 DonnyFL adapter. DonnFL will export his adapters. In function these internal compartments are expansion chambers where the only air path from one chamber to the next is via the tight central bore. This system progressively reduces the driving air pressure behind the pellet as well as the air velocity between the baffles. The net result is a huge reduction is sound. There is a slight difference in the sound signature with and without a pellet, but not in loudness. The extra weight an the end of the barrel does cause a change in barrel droop and POI by 3.5 cm down and left at 20 meters, but not in accuracy and grouping. grouping is the same with and without the moderator mounted. The pellet used during testing was the JSB 25.39 grain Exact King. Muzzle velocity without the moderator was 940 fps and with the moderator is 900 fps and is consistently repeatable.

 

[steve-l]

I would suggest that, instead just put spacers between the washers, get a smaller diameter spacers ( hair curlers are 2cm in diameter) wrap with a sort of screen and cotton until reaches the ID of the silencer tube and you are good to go, just spacers wont suppress/dampening the sound as there is nothing to absorb the sound coming out of the barrel, make sure when wrapping the cotton around the curlers is nice and compressed and very snugly in the tube (not over tight), use cotton roll as it's easy to cut the length of the spacer and normally they are around 1/2" thick. That will damp the sound a lots. Also, sometimes is better use washers with a slightly larger hole, like 8mm, that helps the air/sound flow and expand, instead of compressing and exiting on a smaller whole causing a high pitch sound.

In my experience, using sound absorbing material in the moderator does not work. It decreases expansion chamber volume having the opposite effect of increasing the emitted sound volume.

 

[airgunfans]

I would suggest that, instead just put spacers between the washers, get a smaller diameter spacers ( hair curlers are 2cm in diameter) wrap with a sort of screen and cotton until reaches the ID of the silencer tube and you are good to go, just spacers wont suppress/dampening the sound as there is nothing to absorb the sound coming out of the barrel, make sure when wrapping the cotton around the curlers is nice and compressed and very snugly in the tube (not over tight), use cotton roll as it's easy to cut the length of the spacer and normally they are around 1/2" thick. That will damp the sound a lots. Also, sometimes is better use washers with a slightly larger hole, like 8mm, that helps the air/sound flow and expand, instead of compressing and exiting on a smaller whole causing a high pitch sound.

In my experience, using sound absorbing material in the moderator does not work. It decreases expansion chamber volume having the opposite effect of increasing the emitted sound volume.

Not a serious test but I have tried putting a layer of 5mm thick kitchen cleaning felt on the inner wall of my moderator but it did not help to reduce the sound level at all.

 

[airgunfans]

I also made my own moderator for the same reason you did.....

Thanks for this great info sharing ! May I ask how you find the conical baffles preform relative to flat washers ? I have tried using conical baffles and flat washers in another DIY silencer made for my Alectol pistol but there is not any perceivable difference. In fact I have tried to remove all the internals of the silencer leaving only an empty can but the sound level is more or less the same. Is that your experience also ? 

 

[steve-l]

The conical baffles are a real PIA to make because holding them in a chuck becomes problematic for perfect concentricity between the OD and the bore hole. Do they perform better? I'm not sure by very much, but they are much stiffer and withstand the significant pressure pulse they receive. I made the last moderator in aluminum, but my next will be carbon fiber for the weight issue. In your case using steel makes the whole thing too heavy. This pulse may be powerful enough to destroy a CF baffle if strait. The 354 grams my aluminum one weighs causes the 3.5 cm POI change on the Crown. I will make another in CF and hope to get it down to 200 grams. Adding 8" to the gun length makes the gun a bit unweilding, but that's what quiet costs. If you have a chronometer, please check the loss of velocity your moderator costs. I believe the amount of speed loss is a product of effectiveness. Where the quieter the moderator, the greater the speed attenuation will be. As stated, I lose 40 fps.with this one. I'm curious how much you lose..

I have asked around in different forums what others thought was the cause of the speed loss and I received all kinds of bullpoop theories that made little sense, but I believe the pellet is not slowed by the moderator. I believe the resistance the moderator applies to the column of air in front of the pellet prevents the pellet from achieving the un-moderated speed, at least that's my theory.

On the point of baffle value, yes they do make a significant difference in sound level. I have settled on using 3 baffles. They should not be symmetrically spaced. The first chamber should be about 40% of the internal volume.

 

[airgunmonkey]

I would suggest that, instead just put spacers between the washers, get a smaller diameter spacers ( hair curlers are 2cm in diameter) wrap with a sort of screen and cotton until reaches the ID of the silencer tube and you are good to go, just spacers wont suppress/dampening the sound as there is nothing to absorb the sound coming out of the barrel, make sure when wrapping the cotton around the curlers is nice and compressed and very snugly in the tube (not over tight), use cotton roll as it's easy to cut the length of the spacer and normally they are around 1/2" thick. That will damp the sound a lots. Also, sometimes is better use washers with a slightly larger hole, like 8mm, that helps the air/sound flow and expand, instead of compressing and exiting on a smaller whole causing a high pitch sound.

In my experience, using sound absorbing material in the moderator does not work. It decreases expansion chamber volume having the opposite effect of increasing the emitted sound volume.

That's why I suggest using cotton, it's light and allows the air and sound to expand between the fibers, it has worked for me every time, like some of us, I make my own silencers, not because I can't afford one but I like the work and challenge, I have several rifles and they are quiet as I have close grumpy neighbors, some of my silencers I even used a 20mm OD PVC pipe cutted to the length I drilled a series of holes and wrapped with the screen and cotton, works for me, again it is just a suggestion from me. Most of the airguns silencers manufactures use felt, like DonnyFL, Hugget etc, I like cotton. Using hair curlers it's easier the drill a series of holes on a alu spacer or a PVC pipe, just have to cut to the desire length and wrap them, it's a simple and easy way, if the OP like to play with it, like I do. On a 40mm tube with a hair curler that is 20mm OD, leves +/- 18mm of space (if the tube haas a wall thickness of 2mm) between to wrap with the sound dampening material, is this case cotton wrapped nice and tight.